The following is provided as background solely for the benefit of the reader and is not intended, nor is it to be construed, as prior art to the present invention.
The intraocular lens, which can be surgically implanted in the eye of a patient, has experienced a remarkable history of innovation, each predicated on perceived shortcomings of its predecessor. For instance, the first rigid polymethylmethacrylate (PMMA) lens implanted in the posterior chamber between the iris and the lens by Harold Ridley in 1950 resulted in some relatively serious complications such as decentration or delocalization of the lens due to its size and weight and the frequent occurrence of uveitis. In 1953, a few short years after the introduction of the Ridley lens, anterior chamber, the space between the cornea and the iris, implantable lenses were brought to market. These were held in place in the anterior chamber by a closed loop, which, as the name suggests, comprised a string-like piece of non-optic polymeric material attached at both ends to the lens proper, thus forming a loop. The early closed loops, like the lens itself, were rigid. Unfortunately, these lenses, due to their instability in the anterior capsule, were as prone to complications as the Ridley lens with bullous keratopathy, cystoid macular edema and glaucoma being the more common complications observed. To correct the instability problem, anterior chamber lenses were developed that relied on the papillary portion of the iris for anatomical fixation. Some lens designs required suturing to the iris, some clipped on. This, however, was found to lead to luxation of the lens when the pupil dilated unexpectedly. In about 1970, the anterior lens was again restructured, this time using a flexible closed-loop construct. Corneal damage, however, continued to be a problem and corneal transplants due to implant-related damage to the cornea were not uncommon. The next innovation in intraocular lens was the flexible open loop anterior chamber lens. As suggested by the name, “open loop” refers to a non-optic peripheral appendage that is attached to the lens proper at only one point, the other end of the loop being free to move about and conform to the surface of the eye. This resolved for the most part the corneal problems associated with intraocular lenses but other complications such as cystoid macular oedema continued to occur.
In about 1975, the posterior chamber lens was introduced. As mentioned previously, the posterior chamber is the space behind the iris and in front of the eye's natural lens. While the optic portion of this lens, like its predecessors, was made of PMMA, its haptics, that is, the non-optic portion of the lens at the periphery used to hold the lens in place as exemplified by the closed and open loop configurations, were often made of such materials as polyamide or polypropylene. While these lenses offered numerous advantages such as fewer corneal problems, less retinal detachment and less uveitis-glaucoma-hyphaema (UGH) syndrome, they still required relatively large incisions, approaching 6 mm in length, for implantation. Driven by the advent of phacoemulsion technology for the removal of lenses clouded by cataracts through very small incisions in the eye, foldable intraocular lenses were developed. These lenses can be folded to fit through the same incision used to remove the natural lens, i.e., as small as 2.5-3.0 mm, and then unfolded to operational size once within the eye. One of the predominant types of foldable intraocular lenses presently in use is the so-called hydrophobic acrylic lens as exemplified by the Alcon Acrysof® lens. These lenses, while relatively new in ophthalmology, seem to be avoiding many, if not most, of the complications of their predecessors.
A problem has arisen with the hydrophobic acrylic lenses, however. The lenses, when implanted in a patient's eye, tend over time to form small, light reflective regions in their structure called “glistenings.” While the actual cause of glistenings remains unresolved, one theory is that even though these lenses are nominally hydrophobic, over time some water is able to enter into vacuoles in the polymeric matrix comprising the lens thereby changing the refractive index of the lens at those points, which change appears as reflective spots or “glistenings.” While there is still some debate over the effect of glistenings at the clinical level, there remains a concern that in worse case scenarios a loss of visual acuity might occur that may require excision of the lens. Even at lesser levels, glistenings can cause glare and other annoyances to patients who have had a hydrophobic intraocular lens implanted.
Thus, there is a need for an acrylic foldable intraocular lens that either is not susceptible to glistenings at all or has a substantially reduced tendency to form glistenings. The present invention provides such a lens.